In the refining of a metal melt, especially a ferrous metal melt such as an iron melt to produce steel, it is common or desirable to introduce substantial amounts of scrap metal, alloying solids and other solid materials, which, relative to the molten metal, constitute cooling agents.
Since a sudden drop in the temperature of the melt is undesirable, uneconomical and may interfere with the progress of the refining process, there have been various proposals for resolving the problem.
The obvious solution is, of course, to limit the amount of the cooling solids which are introduced at any time into the melt. This has the disadvantage of interfering with productivity since effective use of the plant requires that the charging capacity for scrap metal in the melt be increased rather than reduced.
Since scrap metal constitutes most of the solid cooling material which may be introduced into the melt, it has been proposed to preheat the scrap metal using gas or heavy oil burners or even plasma burners. All these operations are expensive, difficult to carry out and require separate pretreatment of the scrap metal and the transfer of hot scrap metal to the melt.
It has also been proposed to incorporate into the metal being refined, energy-generating materials. Thus, for example an excess of carbon may be provided so that, during the refining process the carbon gases can react exothermically with the refining oxygen and thereby generate additional heat which, in turn, can compensate for the cooling action of the large quantities of scrap which can be introduced.
Thus earlier systems have proposed the topblowing or bottomblowing of carbon particles into the melt, e.g. by entrainment with an inert gas.
While, as some of the systems described in the aforementioned copending applications demonstrate, there have been significant improvements in the bottomblowing of a melt with solids entrained in a gas stream, in general, the incorporation of solids into a melt by a gas injected from the bottom can create a problem with respect to clogging of the gas and particle feeders which can only be solved by introducing especially large quantities of gas continuously from the bottom, thereby running the risk of cooling the melt with this gas and reducing the solubilization of carbon because of such local cooling phenomena.
Earlier top blowing systems (see French patent publication No. 79.16626) utilize a carbon carrier, namely calcium carbide entrained in the refining oxygen, the calcium carbide having a particle size of 0.01 to 1 mm.
Apparently, under the circumstances described in this publication, the oxidation of the calcium carbide by the refining oxygen before the penetration of the calcium carbide into the melt does not occur. Apparently this is a consequence of the sudden drop in temperature, counteracting the tendency to such a reaction which occurs as the refining oxygen emerges from the blowing nozzle.
While the use of calcium carbide is successful in enabling the melt to accept large quantities of scrap metal which have not been preheated, this system has the disadvantage that the fabrication of calcium carbide is an energy consuming process such that the calcium carbide is costly.
When attempts are made to carry out the process of this French publication with anthracite powder and other coal dusts or carbonaceous materials, an intensive reaction outside the melt appears to occur which is detrimental to the lining of the vessels, gas ducting equipment and the like. Furthermore the slag above the melt foams excessively and there is a danger that the refining vessel will overflow or that its contents will spatter.